In the United States umbilical artery catheters (UACs) are the central line of choice in a neonatal ICU for obtaining arterial blood gases. UACs are also used to monitor internal blood pressure through a transducer attached to the infusing fluids line. UACs are relatively easy to place in a newborn because the umbilical cord is freshly cut and the artery is easy to see. When a neonate is critically ill or premature, frequent arterial blood gases are needed to assess their respiratory status. When an infant is on a ventilator, the blood gas results are used to adjust the ventilator settings appropriately. UACs are only placed in infants needing frequent arterial blood gases, not just to get normal labs or monitor the infant's blood pressure.
A UAC line setup is shown in FIG. 1 and consists of the following: a UAC catheter 22 inserted into a neonate's umbilical artery, a stopcock 24 with a female port 66, an IV line for infusing fluids 26, and a transducer for monitoring blood pressure (not shown). The system through the catheter is filled with saline solution and heparin. Slow dripping of saline and heparin into the patient prevents clotting of blood in the catheter and therefore keeps the line open. The infusing fluids usually run at 0.5 cc-1 cc per hour in a neonate.
A currently used process for obtaining blood samples from the female port 66 on the stopcock is described below. Shift the stopcock off to infusing fluids (FIG. 1B); this opens the fluid path between the catheter and the syringe. Draw 0.5 cc-1.5 cc of blood into the empty 3 cc syringe 28 to clear the UAC of all infusing fluids and bring whole blood to the female port of the stopcock. Shift the stopcock off to all lines (FIG. 1C). Remove this syringe and keep it sterile. Place a lcc heparinized syringe on the stopcock. Shift the stopcock off to the infusing fluids. Draw back on the lcc syringe until a 0.1-0.3 cc sample is obtained. Shift the stopcock off to all lines. Remove the 1 cc syringe and replace the blood filled 3 cc syringe onto the stopcock. Shift the stopcock off to the infusing fluids. Aspirate on the syringe to remove any air that may be trapped, then give the blood back to the patient. Shift the stopcock off to all lines. Remove the 3cc syringe and place a 3 cc flush filled syringe onto the stopcock. Shift the stopcock off to the infusing fluids. Aspirate on the syringe to remove any air, then flush to clear the line of blood, usually 0.5-1 cc. Shift stopcock off to all lines. Remove the 3 cc flush syringe and place a sterile, empty 3 cc syringe on the stopcock. Shift the stopcock off to the syringe. Now the system is open again to the slow dripping of saline and heparin and ready for the next blood draw.
The foregoing procedure has obvious disadvantages. A large number of manipulative steps are required to carry out the procedure. More important are the many chances for contamination of the female port of the stopcock during the frequent switching of syringes. Neonates can die very quickly and suddenly from sepsis even in a neonatal intensive care setting. The syringe most likely to become contaminated is the first 3 cc syringe used to clear the line of infusing fluids prior to blood sampling. If this syringe becomes contaminated it must be thrown away along with the infant's blood. One may think that 5 0.5 cc-1.5 cc of blood is not that much, but in a 1 to 4 pound infant it is. The blood volume for a neonate is approximately 90 cc/kg* (or 41 cc/lb). For premature infants whose blood volume can be as little as 50 cc or less, anemia is commonly caused by blood draws.* Infants can go into shock if they lose 1/4 or more of their blood volume. For example, a micro-premier weighing 500 grams (1 pound 2 ounces) would only have to lose about 11 cc or a little more than 2 teaspoons of blood to go into shock. Infants need the most blood samples taken when they are acutely ill. Arterial blood gases will be drawn every 1/2 hour to every 4 hours when an infant is on a ventilator. So, one can easily see how often an infant is exposed to contamination and the risk of blood loss.
When using the above procedure for blood sampling, one must be sure to shift the stopcock off to all lines before changing syringes or blood will run out of the open port. Obviously this would lead to more blood loss for the neonate.
An apparatus for drawing arterial blood samples and monitoring blood pressure has been introduced to neonatal intensive care, but seems to be designed with pediatrics or adults in mind. Please see FIG. 2.
The procedure for drawing from this apparatus is as follows. First make sure a 10 cc flush syringe 40 has 3-8 cc of flush solution in it. There can not be more than 8cc of flush in this syringe or there may not be room to draw back enough blood to clear the line for blood sampling. Shift stopcock 34 so it is off to the infusing fluids. Aspirate on syringe 40 until blood reaches a black line 38 on a tubing 36 to clear the line of infusing fluids and bring whole blood to an access port 30. Shift stopcock 34 so it is off to everything. Clean an access port 30 and introduce a shrouded needle with a 1 cc heparinized syringe into it. The shrouded needle locks onto the port Shift stopcock 34 so it is off to the infusing fluids. Withdraw 0.1-0.3 cc of blood into the 1 cc syringe and remove it from the sample portMove back to syringe 40 and flush the line to clear it of blood, up to 4 cc of flush is needed at times. Shift stopcock 34 off to syringe 40, as it is in FIG. 2, and the connection between the infusing fluids and the UAC is open again.
While this apparatus has greatly decreased the chance of contamination of the line, it has to also caused many new problems. It is very bulky and spread out. For this reason, many nurses will place an additional stopcock 24 on the line (as I did in FIG. 2) and continue drawing blood samples with the procedure described previously. Therefore, the apparatus is used only for transducing the blood pressure and the original contamination risks are still a factor.
Another significant drawback of the apparatus is 2.5 cc of blood has to be aspirated to reach the black line 38. This is compared to 0.5 cc-1.5 cc drawn off with the first procedure described. Also, more flush is needed to clear the line after blood sampling because the apparatus is so spread out. Although it is designed to require 1 cc of flush, the flush needed to clear the line of blood can be up to 4 cc. More blood drawn off and more flush needed to clear the line is very significant in premature babies. Premature infants and especially micro-premies are most critically ill and most prone to intracranial bleeds during the first few days of life. Intracranial bleeds can be caused by just positioning a premature infant wrong. More important in this instance, intracranial bleeds can be caused by sudden fluid shifts such as taking off or adding fluid to their system suddenly. Also during the first few days of life, when they are most critically ill, is when they need the most arterial blood draws to assess respiratory status.
When an infant needs a bolus of fluid, that fluid is given at 10 cc per kilogram over at least 20 minutes to protect their brain. For example, a 500 kilogram infant would receive a 5 cc bolus over at least 20 minutes. With the current apparatus 2.5 cc of fluid is drawn off the infant. Then that 2.5 cc plus 1 cc-4 cc of flush is added to the infant over a matter of seconds.
If more than the minimal amount of flush is used with a neonate, over a short period of time electrolyte imbalances can occur. Electrolyte imbalances can cause many problems such as cardiac dysrythmias, bronchopulmonary dysplasia, seizures, etc.
With a 10 cc syringe it is difficult to assess exactly how much flush is used. The larger the syringe the less accurate the readings. In the neonatal ICU, input and output are recorded to the tenths and sometimes hundredths (0.0-0.00).
Also, some neonatal ICU's standard operating procedure states a clean flush should be used with each blood drawing procedure from a UAC. Obviously this is not happening with this apparatus. Or the system is being opened each time risking contamination to change the flush syringe at connection 41. Also, so much flush is used the flush syringe needs changed frequently.
Another risk with this apparatus is air in the line. For example, the person performing the blood draw happens to place the sample syringe on the sample port prior to clearing the line of infusing fluids. The result is air being drawn through the syringe and into the line as a syringe 40 is aspirated on to bring whole blood to the sampling site. This would lead to changing the whole system out, or drawing the air (and blood and saline) out into several syringes until the line is cleared of air, and then flushing the line with a new flush filled syringe. Either response chosen to clear the air in the line leads to a considerable amount of the infant's blood being thrown away.
If an additional stopcock is added to the apparatus, as I said some nurses will do, the stopcock's controls can be positioned incorrectly leading to flush filled blood in line 36 being drawn into the blood sampling syringe. This leads to skewed lab results and more blood being drawn to repeat the labs.
The above apparatus has the blood collecting unit permanently incorporated into the fluid line with the blood pressure transducer. If the apparatus is used on a peripheral arterial line of a neonate, only the transducer is used from the system to monitor blood pressure. The blood drawing part of the apparatus can not be used and is wasted on a peripheral arterial line in a neonate because blood can not be aspirated out. If blood is aspirated out of a peripheral arterial line in a neonate arterial damage can occur, possibly leading to the permanent loss of a hand or foot.
Neither of the current procedures used for blood sampling are appropriate for the neonatal intensive care.